In a related-art derailment detection apparatus for an elevator, first and second conductive lines are stretched in parallel to counterweight guide rails. Contact arms each are mounted to a counterweight so as to be opposed to the first and second conductive lines. Each of the contact arms is brought into contact with the first or the second conductive line when the counterweight is displaced forward, backward, rightward, or leftward. Contact of each of the contact arms with the first or the second conductive line is detected by a detection unit (for example, see Patent Literature 1).
Further, in another related-art derailment detection apparatus, first and second contact elements are installed on a counterweight. The first contact element surrounds a first conductive line, and is brought into contact with the first conductive line when the counterweight derails from counterweight guide rails. The second contact element surrounds a second conductive line, and is brought into contact with the second conductive line when the counterweight derails from the counterweight guide rails. Further, the first conductive line is set at a positive potential, and the second conductive line is set at a ground potential. A detection unit detects derailment of an ascending/descending body from the guide rails based on whether or not conduction between the first contact element and the first conductive line is established (for example, see Patent Literature 2).